Internal combustion engines convert chemical energy from a fuel into mechanical energy. The fuel may be petroleum-based, natural gas, another combustible material, or a combination thereof. Most internal combustion engines inject an air-fuel mixture into one or more cylinders. The fuel ignites to generate rapidly expanding gases that actuate a piston in the cylinder. The fuel may be ignited by compression such as in a diesel engine or through some type of spark such as the spark plug in a gasoline engine. The piston usually is connected to a crankshaft or similar device for converting the reciprocating motion of the piston into rotational motion. The rotational motion from the crankshaft may be used to propel a vehicle, operate a pump or an electrical generator, or perform other work. A vehicle may be a truck, an automobile, a boat, or the like.
Many internal combustion engines use a fuel injection system to deliver fuel to the cylinders. A fuel injector usually sprays a measured amount of fuel in the cylinder. In diesel engines, the fuel pressure typically is increased for injecting the fuel near or at the end of the compression cycle. Fuel injectors for diesel engines usually have an actuating mechanism such as a piston to increase the pressure of the fuel. The actuating mechanism in many fuel injectors is hydraulically activated. Some diesel engines use hydraulically activated electronically controlled unit injection (HEUI) fuel injectors.
HEUI fuel injectors usually require high-pressure hydraulic fluid or oil for proper operation. The oil pressure varies in the range of about in the range of about 500 psi (3 MPa) through about 4,500 psi (31 MPa) depending upon the operating mode and condition of the engine. In a typical HEUI fuel injection system, a low-pressure pump moves oil from an oil reservoir to a high-pressure pump. The high-pressure pump provides high pressure oil to an oil rail or manifold, which supplies the high pressure oil to the fuel injectors in the engine.
Many HEUI fuel injection systems use an injection pressure regulator (IPR) to control the output pressure of the high-pressure pump. The pressure control includes the amount, timing, and changes of pressure in response to the engine mode and operating conditions. An IPR is an electrically-controlled pressure release valve that typically is placed on the outlet side of the high-pressure oil pump. The IPR usually has a solenoid, a poppet valve, and a spool valve. When energized, the solenoid operates the poppet valve to control the amount of oil entering a spool chamber in the spool valve. The pressure of the oil in the spool chamber moves a spool to open and close drain ports in the spool valve. The drain ports are connected to a return circuit to the oil reservoir for the engine. The solenoid controls the spool valve in response to control signals from a vehicle's on-board computer or other electronics. When the oil pressure is too high, the IPR opens the drain ports in the spool valve to let oil pass through the drain port and into the return circuit. When the oil pressure is too-low or there is a high-pressure demand from the engine, the IPR closes the drain ports to block the exit of oil through the drain ports. The drain ports may be closed, partially open, or fully open at different times to maintain the desired oil pressures during operation of the engine.
An internal pressure regulator (IPR) may be replaced when operating improperly. An IPR may be replaced during engine repairs or maintenance even when working properly. If there are difficulties starting the engine or concerns with the high-pressure pump, many service technicians replace the IPR as part of a general diagnostic approach to address these difficulties and concerns. If the new IPR does not address the difficulties or concerns, the old IPR is not reinstalled even though it may work properly. The old IPR may not be tested to determine whether it works properly. The replacement of an IPR that works properly may increase the operating and/or maintenance costs of the engine.